FLOOD08354

• County: Boulder
• Community: Lafayette
• Stream Name: Coal Creek , Waneka Reservoir
• Basin: South Platte
• Title: Major Basinwide Planning
• Date: 12/1/1980
• Prepared For: Boulder County
• Prepared By: Camp Dresser & McKee
• Floodplain - Doc Type: Floodplain Report/Masterplan

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areas throughout Sub-basins 6A, 6B, IDA and 11 (refer to Drawing B),
Developments in Sub-basins 6A and IDA have eliminated the historic drainageway,
and the existing channels in Sub-basins IDA and 11 are not adequate to convey
the 100-year future condition fl ow through the roobil e home development. In the
lower portions of Sub-basins 1A and 2A, the inadequate culverts under the
Burl i ngton Rail road track causes the fl ow to pond in the agricultural area
upstream of the tracks. The flow from the older sections of Lafayette
(primarily, that area defined by Basins 5B and 5C on Drawing B), are conveyed to
downstream areas via the Emma Street Ditch and the Burlington Ditch. However,
at the Burlington Railroad, inadequate culverts force the flow to roove overland,
eastward through Sub-basin 5A.

storm runoff conveyance system is needed through or around these areas to
rel ieve the flooding potential that developing upstream tributary areas will

create.

Floodplain Management

The purpose of floodplain management is to: (1) protect the public's health,
safety and general welfare; (2) eliminate or minimize flood hazards and flood
damages; (3) promote the wise use of potential flood zones or floodplains; and
(4) provide for the preservation of floodways and floodplain storage areas in
order to protect those downstream from increased fl oodi ng,

The damages which can be expected with the occurrence of a 100-year frequency
storm would depend upon the type of development that may occur in the future.
In agricultural areas, damages would consist primarily of debris accumulation,
silt deposition and erosion which could adversely affect its use, Depending
upon the frequency and magnitude of storm flows, erosion of soils and debris
buildup will be likely to occur and possibly render localized areas of
agricultural land useless for crop production.

The 100-year fl ooded areas presented in Figure 5 have been prepared in order to
guide the major drainageway planning process, so that future major storm
drainage systems will el iminate future potential flooding damages. Along with
addressi ng future development needs to control damages in the potenti al fl ooded
areas presented in Figure 5, it is important that all new development conform to
the Storm Drainage Design and Technical Criteria developed for the City of
Lafayette and Surrounding Boulder County. The land development process has to
provide for adequate drainage planning to mitigate the potential flooding
damages to existing and future development.

In areas where urban uses develop, damages typical to fl ooding can be expected.
Such damages cons ist of silt and debri s depos it i on, ba sement or fi rst fl oor
flooding, culvert and washouts and undermining of street and sidewalks.
Temporary closures of commercal or industrial areas causing loss of business,
and closure of roadways could al so occur if storm flow systems are not provided,
As shown on the Flooded Area Map, mobile homes and single family residences in
the area of South Boulder Road and North 120th Road and single-family residences
in Centaur Vill age (Sub-basi n 9A), are located in projected fl ood zones. A

The Basinwide Plan drawings were presented to illustrate means of minimizing
flood hazards and fl ood damages, Improvements made to the drai nageway for a
flood frequency of less than the 100-year event have to be made with the
understanding that there may be a residual flood prone area. Floodplains formed
by storm water runoff are the result of natural processes and the fl oodpl ai ns
should not be used for any human occupied structures without providing needed
costly compensatory control measures. Developers and governing agencies need to

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